We will continue work on cytoplasmic actin, myosin and associated proteins using both biochemical and morphological methods to study their relation to cellular movements. We will use new labeled antibody methods to determine the ultrastructural distribution of the major cytoplasmic contractile proteins during cell division, phagocytosis, and platelet activation. We will isolate the major contractile proteins from the isolated intestinal brush border, localize these proteins with labeled antibodies by electron microscopy, analyze the in vivo motility of the microvilli and search for the protein linking the contractile apparatus to the surrounding membrane. To further our understanding of the control of movement, we will isolate cofactor protein from vertebrate cells and study the mechanism by which it stimulates actomyosin ATPase activity. We will complete our analysis of the factors influencing the gelation of isolated Acanthamoeba cytoplasm and then study how purified gelation factors can account for the properties of the complex extract.